This project will investigate the development of children's knowledge concerning people's mental representations of perceived objects and events, conceived as a form of metacognitive and social-cognitive development. Of particular interest to this project is the young child's developing ability to identify and think about the mental representations "appears to be now, under these perceptual conditions" and "really is", both when these representations occur within the self ("appearance-reality" tasks), and when they occur within another person whose perspective differs from the self's (perceptual and conceptual perspective-taking tasks). Recent research by the applicant suggests that many 3-year-old children show surprisingly profound and hard to overcome difficulties in thinking about how things presently appear to them and how they really and enduringly are, when the appearance and the reality differ. Many of the proposed studies are designed to try to explain these difficulties, and, more generally, to provide additional insight into the early development of knowledge about the appearance-reality distinction and related competencies. Other studies will investigate perspective-taking abilities, and also possible developmental links between these abilities and appearance-reality knowledge.